The aim of this study is to conduct a randomized clinical trial to examine whether systematic exposure to full spectrum bright light can normalize disturbed sleep-wake cycles in Alzheimer's disease patients. In addition, since rest-activity cycles and melatonin secretion are controlled by the "Y" pacemaker (but are not believed to be dependent upon each other), this study may provide valuable information about how AD affects circadian rhythms controlled by the "Y" pacemaker.